It came after Walsh defended the sport earlier this week, saying in a magazine interview that the horses are treated better than "many children".

Battlefront had cleared 10 fences in the John Smith's Fox Hunters' Steeple Chase, the first competitive test of significant course changes and new fence frames designed to improve safety.

The cause of his death has not been confirmed but it is thought Battlefront may have suffered a heart attack. A further five horses fell in the race, although none was significantly injured.

Andrew Tyler, director of Animal Aid, said: "The Aintree authorities and the British Horse Racing Authority have been claiming that major new safety measures and efficiencies would eliminate much of the risk associated with racing on the Grand National course.

"But the Fox Hunters' Chase, in which Battlefront lost his life, was stomach-wrenchingly chaotic from start to finish. Several horses fell or were pulled up, tired and potentially injured. It was both utterly depressing and served as confirmation that the Aintree authorities have got it badly wrong once again."

Battlefront was the 23rd horse to die on the Grand National course since 2000, Animal Aid said.

Aintree bosses made significant alterations to the course after last year's big race was marred by the death of two horses, According To Pete and Synchronised.Aintree said the new fences were "kinder if the horse makes a mistake". The height of the fences remains the same.

John Baker, regional director north west of Jockey Club Racecourses, expressed his sympathies to Battlefront's owners and trainers, adding: "You can never remove all risk from horse racing, as with any sport. However, welfare standards are very high and equine fatalities are rare, with 90,000 runners each year with a fatality rate of just 0.2%."